The overall goal of this study is to elucidate the physiological mechanisms by which short term changes in food intake lead to changes in the central neural drive to the reproductive axis in primate species. Previously, we have shown that brief periods of fasting (i.e., one to two days) lead to a significant suppression of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone secretion in adult male rhesus monkeys and men. Subsequent refeeding of monkeys after a brief period of fasting leads to a rapid and dramatic increase in LH and testosterone secretion within the first hour after meal intake. In the current project, the first specific aim is to identify neuronal systems which may mediate the changes in LH secretion caused by fasting and refeeding. Experiments are examining the role of three specific neural systems in mediating nutrition-induced changes in LH secretion (A) the vagus nerves, (B) noradrenergic pathways, and (C) neuropeptide Y-containing neurons. The second specific aim is to determine the role of insulin and thyroid hormone in causing the suppression of LH secretion during fasting and the restoration of LH secretion during refeeding. The third specific aim is to determine the extent to which the diurnal pattern of LH secretion in the male rhesus monkey is determined by the pattern of daily food intake, and the timecourse with which changes in the pattern of food intake modify the pattern of LH secretion. Information provided by these studies is providing insight into the mechanisms by which reproductive function is suppressed in normal childhood, anorexia nervosa, bulimia nervosa, and with vigorous exercise training, in that these are all conditions where metabolic signals have been proposed to be at least partially responsible for the quiescent state of the reproductive axis.